(1) Field of the Invention
The present invention relates to acoustic transducers. More particularly, the invention relates to a cost-effective and reliable device that simultaneously functions as a barrier for water and an acoustic window for acoustic signals in a water medium.
(2) Description of the Prior Art
Instrumentation/sensor packages for use underwater usually must be waterproof in order to function reliably. In addition to needing a water barrier, acoustic transducer packages used for undersea detection and/or communications further require a reasonable acoustic match through what is called an acoustic window to the surrounding water medium. Transducers operating in the active mode (projecting acoustic signals into ambient water) and/or passive mode (receiving acoustic signals from ambient water) need an acoustic window capable of responsively, bi-directionally passing the acoustic signals to and from the ambient water medium.
Contemporary acoustic windows seal acoustic devices while allowing acoustic signals to pass to the device. The devices typically consist of a minimal layer of water-blocking material such as neoprene, nitrile, or ethylene propylene diene terpolymer (EDPM) rubber and an intermediate layer of acoustically acceptable material such as caster oil or polyurethane. The water-blocking layers described are not good Rho-C matches to water and are therefore applied at a minimal thickness so as not interfere with the signal. The water-blocking layers also require an elevated temperature and pressure cure that can be harmful to the components of the acoustic device. As a result, the water-blocking layer is fabricated as an envelope or boot. The acoustic device is placed inside the water-blocking enclosure which is then backfilled with the Rho-C matching materials described.
Other water-proofing and engineering materials have been applied to acoustic windows to enhance their physical performance. One such application is the bonding of a thin titanium sheet (about 1/31″ thick) to an acoustic array for added impact resistance. Another application is gold plated titanium foil which is wrapped around a polyurethane molded acoustic device and local preamplifier for the purpose of water-proofing and electronic shielding. However, working with titanium is difficult, and without gold plating it is expensive.
One type of acoustic window not to be confused with the invention herein described is the hydrodynamic fairing such a bow dome on a ship or submarine that is placed over an acoustic sensor or array of such sensors. These hydrodynamic fairings typically are freely-flooded with a layer of water between the fairing and the acoustic transducer elements and protect against damage from impact.
Thus, a need exists for a thin layer of etched (chemical or radiation etched) fluoropolymer bonded into potting materials for stopping water permeation in undersea instrumentation packages including acoustic transducers. The layer should be inexpensive and easy to work with and a better waterblocker than neoprene, nitrile, or ethylene propylene diene terpolymer (EDPM) rubber etc.